JPH039592Y2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field of the Invention The present invention relates to a fluororesin-lined steel pipe, which is a steel pipe lined with a fluororesin. This invention relates to a fluororesin-lined steel pipe that does not lift up from the inner peripheral surface of the steel pipe.

Technical background of the invention and its problems In pipes made of metal or general-purpose synthetic resin,
It cannot be used for corrosive fluids due to poor chemical resistance, and scale may adhere to the pipe wall, so fluoroplastic liners are installed on the inner circumferential surface of steel pipes. Steel pipes are used.

For example, in a fluorocarbon resin-lined steel pipe, a polytetrafluoroethylene resin tube having a diameter slightly larger than the inner diameter of the steel pipe is attached to the inner peripheral surface of the steel pipe, and its outer diameter is mechanically changed. The tube is manufactured by drawing it in while squeezing it, and folding the end of the tube back. With the fluororesin-lined steel pipe obtained in this way, when the pressure of the fluid passing inside the lined steel pipe is positive pressure greater than normal pressure, the withstand pressure of the fluororesin-lined steel pipe is dominated by the strength of the steel pipe itself. Because of this, it can withstand quite high pressure,
On the other hand, if the pressure inside the pipe is negative pressure, which is lower than normal pressure, the liner may float up from the inner circumferential surface of the steel pipe, blocking the flow path and causing cracks in the liner. These phenomena appear more conspicuously in large-diameter steel pipes than in small-diameter steel pipes, in thin-walled liners rather than thick-walled liners, and at high temperatures than at low temperatures.

It is known that in order to solve these problems, it is sufficient to increase the thickness of the liner. However, making the liner thicker not only increases cost, but also makes it difficult to fold back the ends.
Another problem is that the liner softens in high-temperature environments, making it unusable under high vacuum conditions. Therefore, in order to perfect the negative pressure resistance, the thickness of the liner must be increased to such an extent that the passage of fluid is obstructed, although this is extreme.

In addition, in order to solve the above-mentioned problems, Japanese Utility Model Publication No. 1064/1986 discloses that a through hole is drilled in a steel pipe with a fluororesin liner provided on the inner peripheral surface, and the liner and the liner are connected through the through hole. A lining steel pipe is disclosed that is configured to maintain a reduced pressure state between the lining and the steel pipe using a vacuum pump and can be used even under negative pressure conditions. However, this lined steel pipe has problems in that a through hole must be bored in the steel pipe and a vacuum pump must be used to use it under negative pressure conditions.

Further, Japanese Utility Model Publication No. 53-51181 discloses an electromagnetic flowmeter in which a liner in which a tubular reinforcing material having a large number of holes is embedded is provided on the inner peripheral surface of the pipe. In this electromagnetic flowmeter, when the liner is made of fluororesin, a perforated plate, which is a tubular reinforcing material having many holes, is inserted into the steel pipe, and the perforated plate is inserted along the inner peripheral surface of the perforated plate. This is a so-called transfusion method in which heat-melting fluororesin is heated to a fluidized state and poured between the cores and the perforated plate and between the perforated plate and the inner peripheral surface of the steel pipe. An injection method such as a molding method or an injection molding method is used.

However, if a liner is formed on the inner circumferential surface of a steel pipe by the method described above, the length of the steel pipe on which the liner is provided is naturally limited. In other words, heat-melting fluororesin has a very high melting temperature and melt viscosity, so if the injection pressure of the fluororesin in a fluid state is low, it takes time to inject it. On the other hand, if the injection pressure of the fluororesin is increased, the steel pipe or core may be destroyed. Therefore, with the above method, a liner can only be formed on a steel pipe with a length of about 1 m, and when lining a steel pipe with a length of 2 to 3 m or more, it is necessary to line a steel pipe with a heat-fusible fluorine material formed into a tube shape in advance. A method is used in which a resin tube is inserted into a steel pipe. However, with the method of using a heat-melting fluororesin tube that is pre-formed into a tube shape, it is not possible to embed a perforated plate as a reinforcing plate inside the resin, and it cannot be used for a long period of time under negative pressure conditions. It is not possible to obtain usable lined steel pipes.

Purpose of the invention The inventors of the present invention conducted extensive research to solve the problems associated with the conventional technology as described above, and found that tetrafluoroethylene resin does not become fluid even when heated to its melting point; Tetrafluoroethylene resin can be used under negative pressure conditions by taking advantage of its ability to strongly adhere to heat-melting fluorocarbon resins such as copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ether (PFA). The inventors have discovered that a fluororesin-lined steel pipe can be obtained in which the liner formed on the inner circumferential surface of the steel pipe does not lift up from the inner circumferential surface of the steel pipe even when used in the pipe, and has completed the present invention.

Summary of the invention The fluororesin-lined steel pipe according to the present invention is a lined steel pipe in which the inner peripheral surface of the steel pipe is coated with a fluororesin liner, the liner comprising: (i) an inner layer made of tetrafluoroethylene resin; , (ii) a plurality of annular bodies provided on the outer peripheral surface of the inner layer at predetermined intervals in the axial direction, and (iii) an outer layer made of tetrafluoroethylene resin provided on the outer peripheral surface of the annular body, The space between the plurality of annular bodies is filled with a heat-melting fluororesin, and the heat-melting fluororesin is provided on at least one of the front and back surfaces of the annular bodies, and the inner layer made of the tetrafluoroethylene resin and The outer layer is characterized by being thermally fused to a heat-melting fluororesin provided on at least one surface of the annular body and between the annular bodies. Note that this annular body may have a plurality of through holes.

In the fluororesin-lined steel pipe according to the present invention, the liner provided on the inner circumferential surface of the steel pipe is composed of an inner layer and an outer layer made of tetrafluoroethylene resin and an annular body provided between them, and the inner layer and outer layer are Because the liner is firmly attached to the heat-melting fluororesin provided on at least one of the front and back surfaces of the annular body and between the annular bodies, the liner remains inside the steel pipe even when used for long periods under negative pressure conditions. It does not rise from the peripheral surface, so there is no need to make the liner thick, and even a thin liner can be used in high-temperature, vacuum lines. Of course, since the annular body is completely covered with the fluororesin, there is no fear of corrosion by the chemical solution or contamination of the fluid.

Specific Description of the Invention The present invention will be described below based on embodiments shown in the drawings.

1 is a steel pipe, and flanges 2 are formed at both ends of this steel pipe 1. The inner peripheral surface of this steel pipe 1 is
It is covered with a liner 3 made of fluororesin.

The liner 3 has a laminated structure, and the inner layer 3
a, an annular body 3b provided on the outer circumferential surface of this inner layer 3a, and an outer layer 3c provided on the outer circumferential surface of this annular body 3b. This liner 3
is provided on the inner circumferential surface of the steel pipe 1 such that the outer circumferential surface of the outer layer 3c is in contact with the inner circumferential surface 4 of the steel pipe 1.

The inner layer 3a is made of tetrafluoroethylene resin (PTFE)
The inner layer 3a is preferably formed into a tube shape in advance. The PTFE tube preferably used as the inner layer 3a is manufactured by, for example, a ram extrusion method or an isostatic molding method, and a long one can be obtained.

A plurality of annular bodies 3b are provided on the outer peripheral surface of the inner layer 3a. This annular body 3b may have a through hole 5. The material of the annular body 3b does not necessarily have to be metal, and may be a ceramic plate, as long as it is not easily deformed by external pressure. The space between adjacent annular bodies 3b is filled with a heat-fusible fluororesin 6a, and a heat-fusible fluororesin layer 6b is formed on the inner peripheral surface of the annular body 3b, and a heat-fusible fluororesin layer 6b is formed on the outer peripheral surface of the annular body 3b. A heat-fusible fluororesin layer 6c is provided. Further, when the annular body 3b has a through hole 5, this through hole 5 is also filled with the heat-melting fluororesin 6d. Examples of the heat-melting fluororesin 6 include a copolymer resin of tetrafluoroethylene and perfluoroalkyl vinyl ether (PFA), a copolymer resin of tetrafluoroethylene and hexafluoropropylene (FEP), and a copolymer resin of tetrafluoroethylene and hexafluoropropylene (FEP). A copolymer resin of ethylene fluoride, propylene hexafluoride, and perfluoroalkyl vinyl ether (EPE) or a copolymer resin of ethylene tetrafluoride and ethylene (ETFE) is used.

An outer layer 3c is provided on the outer peripheral surface of the annular body 3b, and the outer layer 3c is made of tetrafluoroethylene resin like the inner layer 3a. As the outer layer 3c, a polytetrafluoroethylene resin tube (hereinafter referred to as a PTFE tube) can be used as well as the inner layer 3a, but this outer layer 3c is made by winding a stretched PTFE tape around the outer peripheral surface of the annular body 3b.
It can also be formed into a tube shape by heating and firing at a temperature equal to or higher than the melting point of PTFE.
It can also be formed by covering a heat-shrinkable PTFE tube.

In this invention, the inner layer 3a made of tetrafluoroethylene resin is made by utilizing the property of the tetrafluoroethylene resin to firmly fuse with heat-melting fluorocarbon resin such as PFA.
is the heat-melting fluororesin 6a such as PFA that exists between adjacent annular bodies 3b, and the heat-fusible fluororesin 6a that exists in the through-hole 5 when the annular body 3b has a through-hole 5. It is firmly adhered to the fluororesin 6d and the heat-melting fluororesin layer 6b provided on the inner peripheral surface of the annular body 3b, and as a result, the inner layer 3
a is firmly fused to the annular body 3b. Similarly, the outer layer 3c made of polytetrafluoroethylene resin is made of a heat-melting fluororesin 6a existing between adjacent annular bodies 3b, and if the annular bodies 3b are provided with through holes 5, the annular bodies Exists in through hole 5 of 3b
The outer layer 3c is firmly fused to the heat-melting fluororesin 6d such as PFA and the heat-melting fluororesin layer 6c provided on the outer peripheral surface of the annular body 3b. is fused to. In this way, the inner layer 3a and the outer layer 3c form the annular body 3b.
is firmly fused to.

Next, a method for manufacturing a fluororesin-lined steel pipe according to the present invention will be explained.

First, a method for manufacturing the liner 3 used in the present invention will be explained. An inner layer 3a consisting of a tube made of tetrafluoroethylene resin is prepared, a heat-melt resin film such as PFA is wound around the outer circumference of the inner layer 3a, and annular bodies 3b are placed at intervals on the outer circumference of the heat-melt resin film. Open it and insert it, then insert this annular body 3
A thermofusible resin film is wound around the outer peripheral surface of b.
Next, after winding the stretched polytetrafluoroethylene resin film on this hot-melt resin film, this laminate is heated to the melting point of the tetrafluoroethylene resin (327°C).
Heat to above temperature. At this time, the hot melt resin wound around the inner peripheral surface and the outer peripheral surface of the annular body 3b is melted to form hot melt fluororesin layers 6b and 6c, and a portion of this hot melt fluororesin is teeth,
It flows between the adjacent annular bodies 3b and becomes a heat-melting fluororesin 6a, and this annular body 3b also flows into the through hole 5.
If it has, it flows into the through hole 5 and becomes the heat-melting fluororesin 6d. Then, the inner layer 3a and the heat-melting fluororesin layer 6b provided on the inner circumferential surface of the annular body 3b are thermally fused together, and the heat-melting fluororesin 6a existing between the inner layer 3a and the annular body 3b
and the heat-melting fluororesin 6d existing in the through hole 5 of the annular body 3b are thermally fused. at the same time,
The outer layer 3c and the heat-melting fluororesin 6c provided on the outer peripheral surface of the annular body 3b are thermally fused together, and the heat-melting fluororesin 6a existing between the outer layer 3c and the annular body 3b and the annular body The heat-melting fluororesin 6d that has flowed into the through hole 5 of 3b is thermally fused.

In the above liner manufacturing method, the inner layer 3a
is formed longer than the other layers 3b and 3c, and this portion is used as a folded portion for the flange.

The liner 3 obtained in this way is transferred to the steel pipe 1.
The fluororesin-lined steel pipe according to the present invention can be obtained by mechanically drawing the inner layer 3a into the inner layer and folding back both ends of the inner layer 3a, which is longer than the other layers, along the flange 2.

In the method for manufacturing the liner 3 described above, the hot-melt resin film is wound around both the outer circumferential surface of the inner layer 3a and the outer circumferential surface of the annular body 3b. The film may be wound only around either the outer peripheral surface of the inner layer 3a or the outer peripheral surface of the annular body 3b.

Furthermore, in the above method, the space between adjacent annular bodies 3b is filled with fluororesin melted from the heat-melting fluororesin film wound around the outer circumferential surface of the inner layer 3a and the outer circumferential surface of the annular body 3b. By placing a heat-melting fluororesin ring or a heat-melting fluororesin block between adjacent annular bodies 3b in advance, a heat-melting fluororesin 6a is formed between the adjacent annular bodies 3b. You may.

Effects of the invention In the fluororesin-lined steel pipe according to the invention, the liner provided on the inner peripheral surface of the steel pipe is composed of an inner layer and an outer layer made of tetrafluoroethylene resin and an annular body provided between them. The liner is firmly bonded to the heat-melting fluororesin provided on at least one of the front and back surfaces of the annular body and between the annular bodies, so the liner remains stable even when used for long periods under negative pressure conditions. It does not rise up from the inner peripheral surface of the steel pipe, so there is no need to make the liner thick, and even a thin liner can be used in high-temperature, vacuum lines. In addition, the fluororesin-lined steel pipe according to the present invention can be manufactured by drawing a liner made of fluororesin as described above into the steel pipe, so it has the great effect that a long fluororesin-lined steel pipe can be obtained. be. Of course, since the annular body is completely covered with the fluororesin, there is no fear of corrosion by the chemical solution or contamination of the fluid.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a fluororesin-lined steel pipe according to the present invention, and FIG. 2 is an enlarged cross-sectional view of the main part thereof. 1... Steel pipe, 2... Flange, 3... Liner, 3a... Inner layer, 3b... Annular body, 3c... Outer layer, 4... Steel pipe inner peripheral surface, 5... Through hole, 6a, 6
b, 6c, 6d...Thermofusible fluororesin.

Claims (1)

[Claims for Utility Model Registration] (1) A lined steel pipe in which the inner circumferential surface of the steel pipe is covered with a fluororesin liner, the liner comprising: (i) an inner layer made of tetrafluoroethylene resin; (ii) ) a plurality of annular bodies provided on the outer circumferential surface of the inner layer at predetermined intervals in the axial direction; and (iii) an outer layer made of tetrafluoroethylene resin provided on the outer circumferential surface of the annular body; The space between the annular bodies is filled with a heat-melting fluororesin, and the heat-melting fluororesin is provided on at least one of the front and back surfaces of the annular bodies, and the inner layer and outer layer made of the tetrafluoroethylene resin are A fluororesin-lined steel pipe characterized in that the fluororesin-lined steel pipe is heat-sealed to a heat-melting fluororesin provided on at least one surface of an annular body and between the annular bodies. (2) The fluororesin-lined steel pipe according to claim 1, wherein the annular body has a through hole.